Conventional bicycle frames are assemblies built from individual tubes which are secured together by welding, brazing or by using other means for joining the tubes. The individual frame tubes were, early on, designated by their location in relation to the other major components or assemblies used to make up the functioning bicycle. Thus it was that the short frame tube which supported the handlebar assembly and the front forks was referred to as the "head" tube, the tube which supported the seat and connected to the pedal axle support (the bottom bracket) was referred to as the "seat" tube, the tube which joined the seat tube and the head tube was referred to as the "top" tube, the tube which descended from the head tube to the bottom bracket was referred to as the "down" tube, the pair of tubes which descended from the seat tube to the ends of the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "seat stays," and the pair of tubes which connected the bottom bracket to the ends of the seat stays at the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "chain stays."
The multiplicity of connections required to secure these individual structural parts together, combined with the different forces encountered by the bicycle as it is ridden, cause a variety of problems. It is not unusual, for example, for one or more of the joints or connections on a conventional bicycle frame to fail, making the entire frame unsuitable for use until the connection is repaired. For many frames, the cost of straightening the frame and repairing the connection is prohibitive.
Further, the individual tubes are relatively heavy since they are generally made by the extrusion of or by the rolling and seaming of a metal alloy. The manufacture and assembly of these multiple structural parts is also time consuming and costly.
Finally, most conventional bicycle frame tubes have generally circular cross sections, since they are made from standard, commercial tubing. Thus, due both to the shape of the tubes and to the multiplicity of connection joints, conventional frames are not particularly adaptable to improved aerodynamics.
Some of the above problems have been addressed by prior inventors. For example, U.S. Pat. No. 4,513,986 to Trimble provides a monocoque type frame having a stressed, unitary outer skin over internal stiffening ribs and other structural elements. U.S. Pat. No. 3,833,242 to Thompson, Jr. provides a hard exterior skin covering a structural foam interior. These frames may provide aerodynamic advantages over conventional bicycle frames, due to the aerodynamic shape and unitary nature of the outer skin. However, these frames generally require the interconnection of a large number of interior structural support elements such as shear webs, reinforcing angles, reinforcing blocks and strips, and joining blocks, and/or the presence of structural foam in the interior to support the frame, thus sharing certain deficiencies of conventional frames. In addition, while possibly improving aerodynamic performance in forward motion, a stressed skin will increase the frame's sensitivity to cross winds.
Thus, the need exists for a unitary, strong, lightweight bicycle frame which is aerodynamic, easy to construct and adaptable to mass production techniques. The present invention solves these problems by providing a one-piece, generally hollow, aerodynamic bicycle frame requiring no internal structural components, and constructed from inexpensive, lightweight and strong composite materials.